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Inhaled route CHAPTER 37
*
Liquids for nebulization are either solutions or
permanent suspensions. It may be that solutions
are more reliably nebulized and inhaled than
permanent suspensions
*
Caution should be exercised when mixing two
liquids for nebulization in the nebulizer as one
liquid can cause precipitation in the other
*
The peak flow meter is a simple prescribable
device which gives an objective measurement of
lung function, and can be useful from time to
time for asthmatics, e.g. when commencing a
new treatment. It may also be used to aid
self-management of asthma
*
Many asthmatic and COPD patients will have at
least two or three different inhalers. They will
obtain greatest benefit from their inhalers if they
understand something about their condition, the
rationale for the different inhalers and how and
when to use them
*
Pharmacists with an understanding of asthma
and COPD treatment and the correct use of
inhalers can provide advice, education and
training for patients on inhaled therapy which
can markedly improve patients’ quality
of life
409
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Chapter Thirty-Eight
Parenteral products
Derek G. Chapman
38
STUDY POINTS
*
The reasons for parenteral administration
*
The routes available for parenteral administration
*
The various forms and types of parenteral product
*
The design of containers and methods of
administration of parenteral products
*
The formulation and uses of parenteral products
*
Pyrogens
*
Tonicity adjustment
*
Large-volume sterile products
Introduction
Parenteral products are dosage forms that are delivered to the patient by a route outwith the alimentary
canal. The parenteral route of administration is often
used for drugs that cannot be given orally. This may be
because of patient intolerance, the instability of the
drug, or poor absorption of the drug if given by the oral
route. In practice, parenteral products are often
regarded as dosage forms that are implanted, injected
or infused directly into vessels, tissues, tissue spaces
or body compartments. From the site of administration the drug is then transported to the site of action.
With developing technology, parenteral therapy is being used outside the hospital or clinic environment.
Patients are increasingly using it at home and in the
workplace, allowing them to administer their own
medication.
Parenteral therapy is used to:
*
Produce a localized effect
*
Administer drugs if the oral route cannot be used
*
Deliver drugs to the unconscious patient
*
Rapidly correct fluid and electrolyte imbalances
*
Ensure delivery of the drug to the target tissues.
Parenteral injections are either administered directly
into blood for a fast and controlled effect or into
tissues outside the blood vessels for a local or systemic
effect. An injection can be administered intravenously
to rapidly increase the concentration of drug in the
blood plasma, but the concentration soon falls due to
the reversible transfer of the drug from blood plasma
into body tissues, a process known as distribution. The
drug concentration remaining in the blood plasma is
affected both by the administered dose and by the
quantity of drug transferred into body tissues. Thereafter, there is a slower decrease in the drug concentration due to irreversible excretion and metabolism.
An intravenous infusion administers a large volume of
fluid at a slow rate and ensures that the drug enters
the general circulation at a constant rate. In this procedure, the drug concentration in the blood plasma
rises soon after the start of the infusion and achieves a
steady state when the rate of drug addition equals the
rate of drug loss. When infusion is stopped, elimination of the drug from the body by metabolism and/or
excretion generally follows first-order kinetics.
Following subcutaneous and intramuscular injection there is a delay in the systemic effects of the
drug. The delay is due to the time for the drug to first
pass through the epithelial cells and basement membrane that forms the walls of the capillaries before
entering into the blood. This occurs by passive diffusion that is promoted by the concentration gradient
across the capillary wall. Other factors are also important, including the permeability characteristics and
the number of capillaries in the area. Most plasma
solutes pass freely across the capillary walls, while
SECTION FOUR Dispensing and related pharmaceutical practice activities
water-soluble substances such as glucose and amino
acids pass through intercellular aqueous spaces of the
capillary wall. After passing through the capillary wall
the drug concentration in the blood plasma rises to a
peak level and then falls due to distribution to the
tissues followed by metabolism and excretion.
Administration procedures
Intravenous injections and
infusions
Administration by this route provides strict control of
the drug concentration in the circulating blood. The
vein that is selected for administering the formulation
depends on several factors. These include the size of
the delivery needle or catheter, the type and volume
of fluid to be administered and the rate of administering the fluid. The fluids are administered into a
superficial vein, commonly on the back of the hand
or in the internal flexure of the elbow (see Fig. 21.1).
The intravenous route is widely used to administer
parenteral products, but it must not be used to administer water-in-oil emulsions or suspensions.
Subcutaneous injections
the upper arms and the lateral upper hips. This route
is used if the medicine cannot be administered orally.
The drugs are more rapidly and predictably absorbed
than when administered by the oral route. Following
administration, the site of the injection, the body
temperature, age of the patient and the degree of
massaging of the injection site affect drug distribution. However, absorption of the drug after subcutaneous injection is slower and less predictable than
when administered by the intramuscular route.
Intramuscular injections
Small-volume aqueous solutions, solutions in oil and
suspensions are administered directly into the body of
a relaxed muscle (see Fig. 38.1). Several muscle sites
are used for these injections, including the gluteal
muscle in the buttock, the deltoid muscle in the
shoulder and the vastus lateralis of the thigh. In
adults, the gluteal muscle is often used as larger
volumes can be tolerated. In infants and small children, the vastus lateralis of the thigh is usually more
developed than other muscle groups and is thus used.
For rapid absorption of the medicament, the deltoid
muscle in the shoulder is often used.
Other routes of parenteral administration are de-
scribed below.
These are injected into the loose connective and adipose tissue immediately beneath the skin (Fig. 38.1).
Typically, the volume injected does not exceed 1 mL.
Injection sites include the abdomen, the upper back,
Figure 38.1*Injection routes. ID, intradermal; SC, subcutane-
ous; IM, intramuscular.
412
Intradermal injections
A volume of about 0.1 mL is injected into the skin
between the epidermis and the dermis. Absorption
from intradermal injections is slow. This route is often
used for diagnostic tests for allergy or immunity. It is
also used to administer some vaccines.
Intra-arterial injections
The drug is administered directly into an artery. Owing to the fast flow of blood in the artery it is likely
that the drug will be rapidly dispersed throughout the
blood system. However, manipulative difficulties restrict the use of intra-arterial injections but drugs can
be administered by this route to target a specific organ
or tissue that is served by the artery.
Intracardiac injections
These are aqueous solutions that are administered in
emergency directly into a ventricle or the cardiac
muscle for a local effect.
Parenteral products CHAPTER 38
Intraspinal injections
These are aqueous solutions that are injected in
volumes less than 20 mL into particular areas of the
spinal column. They are categorized as intrathecal,
subarachnoid, intracisternal, epidural and peridural
injections. The specific gravity of these injections
may be adjusted to localize the site of action of the
drug.
Intra-articular injections
These are administered as an aqueous solution or suspension into the synovial fluid in a joint cavity. They
are often used for the local administration of antiinflammatory agents.
Products for parenteral use
Parenteral products are sterile formulations that are
administered into the body by various routes including injection, infusion and implantation.
Injections
These are subdivided into small- and large-volume
parenteral fluids. Small-volume parenterals are sterile, pyrogen-free injectable products. They are packaged in volumes up to 100 mL. Small-volume
parenteral fluids are packed as:
*
Single-dose ampoules
*
Multiple-dose vials
*
Prefilled syringes.
Single-dose ampoules
Most small-volume parenterals are currently packaged as either ampoules or vials. Glass ampoules are
thin-walled containers made of Type I borosilicate
glass (see Fig. 27.3). Injections packaged in glass
ampoules are manufactured by filling the product into
the ampoules, which are then heat sealed. To achieve
the quality required of these products, the packaged
solution must be sterile and practically free of particles. These products are typically prepared in clean
room conditions (see Ch. 29). However, the great
concern with using glass ampoules relates to the
hazards of opening them because the product may
become contaminated with glass particles. Opening
is easier with glass ampoules with a weakened neck.
This is achieved by applying a ceramic paint ring to the
ampoule neck. The paint, after a process of heat baking, has the effect of weakening the neck. Even though
the subsequent opening of the ampoules is physically
easier, a large number of glass particles still contaminate the product. Another ampoule design has a score
on the glass at the ampoule neck with a painted dot
marker on the opposing side. These are known as onepoint cut ampoules. They are easier to open, but glass
particles continue to be released when they are
opened.
Plastic ampoules are prepared, filled and sealed by
a procedure known as blow–fill–seal. This is a fourstep continuous procedure in which granules of plastic are heated to a semi-solid state. The plastic is then
blow moulded and formed into ampoules. These containers are filled with the product and immediately
sealed. This system is only used to package simple
solutions. The plastic may take up drug components
from the product. When the ampoule is opened by
rotating the integral plastic closure, few particles are
released into the solution.
Ampoules should have a reliable seal that can be
readily leak tested. A good seal will not deteriorate
during the lifetime of the product. Medicines packaged in ampoules are intended for single use only. As a
result, these products do not contain chemical antimicrobial preservatives. The ampoule must also contain a slight excess volume of product. This is
necessary to allow the nominal injection volume to
be drawn into a syringe.
Multiple-dose vials
These are composed of a thick-walled glass container
that is sealed with a rubber closure. The closure is
kept in position by an aluminium seal that is crimped
to the neck of the glass vial (see Fig. 27.4). These
closures are then covered with a plastic cap. The cap
is removed before a needle, attached to a syringe, is
inserted through the rubber closure to withdraw a
dose of product. The contents of the vial may be
removed in several portions.
The glass vial packaging system has the advantage
of increased dose flexibility and decreased costs per
unit dose. There are also certain disadvantages with
the use of glass vials. Fragments of the closure may
be released into the product when the needle is
inserted through the closure. There is also the risk
of interaction between the product and the closure.
Repeated withdrawal of injection solution from these
413
SECTION FOUR Dispensing and related pharmaceutical practice activities
containers increases the risk of microbial contamination of the product. These products must, therefore,
contain an antimicrobial preservative unless the medicine itself has antimicrobial activity. An example of
such a multidose product is insulin. Each dose is withdrawn from the vial when required and administered
by the patient.
Prefilled syringes
With these devices, the injection solution is aseptically filled into sterile syringes. The packed solution has a
high level of sterility assurance and does not contain
an antimicrobial preservative. The final product is
available for immediate use. Prefilled syringes are expensive and so only limited products are packaged in
this way.
Administration of small-volume
parenteral products
Hypodermic syringes and needles are extensively
used for administering small volumes of parenteral
formulations to the patient. These syringes have been
sterilized by ethylene oxide gas or, occasionally, by
gamma irradiation following packaging. Various sizes
of hypodermic syringes are available. They are composed of a barrel, having a graduated scale, together
with a plunger and a headpiece, known as a piston
(Fig. 38.2). These components are often made of
polypropylene, although the piston could be made
of medical grade rubber.
Formulation of parenteral products
Vehicles for injections
The drug is generally present in an injection in low
concentration. The vehicle provides the highest proportion of the formulation and should not be toxic nor
have any therapeutic activity.
Mains water often contains a wide variety of contaminants such as electrolytes, organisms and particulate matter, and dissolved gases, such as carbon
dioxide and chlorine. The wide variety of these contaminants causes a problem in the preparation of water for use in injections. This is called ‘water for
injections’ and must be used as the vehicle for parenteral products. It is often used to prepare ophthalmic
products but these could be made using purified
water.
Water for injections
Water for injections is the most extensively used
vehicle in parenteral formulations. Water for injections is well tolerated by the body and ionizable
electrolytes readily dissolve in wat er. Water for
injections must be free of pyrogens. It must also
have a high level of chemical purity. The British
Pharmacopoeia (BP; 2007) considers that water
for injections can only be prepared by distillation
in order to produce a consistent supply of the
required quality of water.
Figure 38.2*Hypodermic syringe for single use.
414
Preparation of water for injections
The usual method of preparing water for injections in
Europe and North America is distillation. While other
processes can achieve a similar quality of product,
these alternative systems cannot produce a consistent
water quality. The source water used in the preparation of water for injections by distillation is usually
potable water. This water varies in quality and may be
contaminated with dissolved gases, suspended minerals and organic substances, mineral salts, chemicals,
endotoxins and microorganisms. The high standard
required of water for injections is only achieved if
the quality of the source water is improved by suitable
pretreatment before it is supplied as feed water
for final processing. The pretreatment of the source
water usually involves:
*
Chemical softening
*
Filtration
*
De-ionization
*
pH adjustment.
The water is then treated by reverse osmosis to yield
purified water. This water is often used as the feed
water for distillation and has a low silica content and a
low total organic carbon content. A wide variety of
designs of still are used in the production of water for
injections. These stills are typically made of stainless
steel, although chemically resistant glass could be
used.
The single effect still is used to produce volumes
less than 90 L/h. This usually fulfils the demands of
small-scale production as required by a hospital pharmacy. The single effect still requires de-ionized feed
water and has three main structural components:
*
An evaporator containing the heater
*
A vapour-liquid disengaging section
*
A condenser.
When this still is functioning, the feed water in the
horizontal evaporator is heated. Steam is produced at
atmospheric pressure and at slow velocity. Some
steam will condense before it enters a vertical vapourliquid disengaging unit that is attached to the
horizontal evaporator. Baffle plates at the base of
the vapour-liquid unit reduce the risk of water droplets being carried in the steam into this unit. The
water droplets and the non-volatile impurities are
returned to the water in the evaporator. The vapourliquid disengaging unit often contains a centrifugal
device that spins the steam as it rises in this unit. This
has the effect of throwing entrapped water droplets in
the steam onto the wall of this vertical cylindrical
section where it condenses and returns to the evaporator. Only pure steam exits from this unit into the
condenser where the heat of vaporization is removed
and converts the water vapour to the liquid distillate.
Only stills designed to produce high purity water may
be used in the production of water for injections.
In operation, the first portion of the distillate must
be discarded. The remainder is collected in a suitable
storage vessel. Freshly collected distillate is usually
free of microbial contaminants and should contain
not more than 0.25 international units of endotoxin
per mL as determined by the bacterial endotoxin test
(see later). However, the distillate is regularly sampled and tested for microbial contamination. It is acceptable if there are fewer than 10 organisms per
100 mL present at any instance; no Pseudomonas bacteria should be present. To ensure that the distillate is
Parenteral products CHAPTER 38
of a suitable purity, the electrical conductivity of the
distillate is measured. This measurement is used as an
indicator of the quality of ionizable materials in the
collected water. The electrical conductance should be
less than 1.1 mS/cm when measured at 20
C. However, the measurement of electrical conductivity alone
as an indicator of water quality can be misleading, as it
does not detect silica in the distillate. To conform with
the quality standards of the BP (2007) and the Euro-
pean Pharmacopoeia (EP; 2007), the distillate will also
have the following quality limits:
Total organic carbon Not more than 0.5 mg per litre
Chlorides Not more than 0.5 parts
per million (p.p.m.)
Ammonium Not more than 0.2 p.p.m.
Nitrates Not more than 0.2 p.p.m.
Heavy metals Not more than 0.1 p.p.m.
Oxidizable substances Not more than 5 p.p.m.
pH
5.0–7.0
Care is required in handling the freshly collected
distillate as it is subject to microbial contamination
during storage and distribution. Two systems are
commonly used for the storage of water for injections:
batch storage and dynamic storage.
Batch storage
With this system the water for injections is stored as a
batch of discrete unit volumes which may be sterilized. Quality control tests are performed on this
batch. Only after the batch is identified as being of
suitable quality is it released for use. This system
provides maximum product accountability before
use. It is, however, an expensive storage system.
Dynamic storage
With this system the storage tank is a surge tank,
usually made of quality polished stainless steel. As
the level of water for injections in the tank falls then
more water for injections is produced and filled into
the tank. The fresh water for injections mixes with
water remaining in the tank. This system is cheaper
and simpler to operate than batch storage. However,
it does lack batch accountability and the water may
become contaminated through corrosion of the steel
tank. Owing to the potential problem with Gramnegative bacterial contamination, it is important that
the distillate is stored at 80
growth. Heating the water in the tank is achieved with
a steam-heated jacket around the tank.
C to prevent bacterial
415
SECTION FOUR Dispensing and related pharmaceutical practice activities
Surge tanks require sterilization at timed intervals.
They are fitted with a filter vent used to equilibrate
the tank pressure during filling and emptying the tank.
The filter prevents airborne bacterial contamination
of the water for injections within the tank.
Distribution
A loop distribution system may be used to deliver the
water for injections to the point of use. The water in
the distributionsystem can becomecontaminated with
organisms. As a result, the water in the stainless steel
pipes is constantly circulated from the tank to avoid
stagnation and to maintain the temperature. This
distribution system has one major disadvantage in that
the point of use may not require high-temperature
water. Thus a cooling system may be fitted close to
the point of use. Microbial growth may then occur in
the cooled water.
Sterilized water for injections
This is prepared by packing a volume of water for
injections in sealed containers. These containers are
then moist-heat sterilized which yields a sterile product that remains free of pyrogens. Sterilized water for
injections is used to dissolve or dilute parenteral preparations before administration to the patient.
Pyrogens
Water is potentially the greatest source of pyrogens in
parenteral products. Untreated pyrogenic water is
contaminated with pyrogens and these must be removed before the water can be used in parenteral
products. This is achieved in the preparation of water
as a vehicle for injections by distillation in the UK.
Pyrogens are fever-producing substances. The injection of distilled water may produce a rise in body
temperature if it contains pyrogens, while water that
is free of this effect is described as apyrogenic.
Microbial pyrogens arise from components of
Gram-negative and Gram-positive bacteria, fungi
and viruses. Non-microbial pyrogens, such as some
steroids and plasma components, also produce a pyrogenic response if injected. The most important
pyrogens in pharmacy products are high molecular
weight endotoxins that are found in the outer membrane of Gram-negative bacteria. Therefore endotoxins potentially exist in all situations harbouring
bacteria.
Freshly prepared parenteral products must not be
contaminated with organisms that could produce
pyrogens. They must be prepared in conditions that
reduce microbial contamination because bacteria contaminating aqueous solutions can release endotoxins.
Contaminated solutions will become more pyrogenic
with the passage of time. Therefore, these products
must be sterilized shortly after preparation.
Endotoxins produce significant physiological
changes when injected. Their detection and elimination is very important for manufacturers of parenteral
products.
Nature of endotoxins
Endotoxins isolated from the out er membrane of
Gram-negative bacteria are composed of three
areas. The inner region is composed of lipid A that
is linked to a central polysaccharide core. This polysaccharide core is joined to long projections known
as the O-antigenic side chains. Lipid A is responsible
for most of the biological activity of endotoxin. By
itself it is not very soluble in water. However, it is
joined to a core polysaccharide by an eight-carbon
sugar that acts as a solute carrier for the lipid A in
aqueous solutions.
The molecular weight of endotoxin is important in
determining its biological activity. In a pure aqueous
environment, endotoxin has a relative molecular mass
of about 10
6
. This is equivalent to the relative molecular mass of a virus particle and is the most common
size of endotoxin found in large-volume parenteral
formulations. In the presence of magnesium and calcium, the endotoxin forms bilayer sheets or vesicles
with a diameter of about 0.1 mm. These small structures can easily pass through a 0.22 mm membrane
filter. This size of filter is commonly used in the production of pharmacy products.
Biological activity of pyrogens
The injection of endotoxins and other pyrogens can
produce many physiological effects. The most important arising from the use of pharmacy products is the
pyrogenic effect, where the lipid A directly affects
the thermoregulatory centres in the brain. At high
dose levels, endotoxin will also:
*
Activate the coagulation system
*
Alter carbohydrate and lipid metabolism
*
Produce platelet aggregation
*
Produce shock and ultimately death.
416
Parenteral products CHAPTER 38
As pyrogens can produce these toxic effects, they
should never be knowingly injected. Their detection
and elimination is very important for the production
of parenteral products. The contamination of largevolume parenteral solutions with pyrogens is especially serious, owing to the large volumes that are administered to seriously ill patients.
Although endotoxins are the predominant pyrogen
in parenteral formulations, other pyrogenic substances also exist. These agents include peptidoglycan, from Gram-positive bacteria, and bacterial
exotoxins, as evidenced by the erythrogenic response
produced by Streptococcus group A organisms which
cause the skin to turn red. Viruses induce a pyrogenic
response that often appears like the fever induced
by the common cold virus. Moulds and yeasts also
produce a pyrogenic effect following intravenous
injection.
Tests for pyrogens
The rabbit test included in the BP (2007) and in the
EP (2007) is very similar to the original rabbit test
included in the 1948 edition of the BP. However, in
recent times, alternative tests for bacterial endotoxins
have been extensively used. The rabbit test that is
used to identify the presence of a wide range of pyrogens does have problems for testing pharmacy products. It is an expensive and slow test that is difficult
to perform even in specialized test centres. The bacterial endotoxin test is a specific test for endotoxins of
bacterial origin. Bacterial endotoxin is the main pyrogen found in parenteral products and the test is
carried out on both the components and the final
parenteral products.
types, known as: the gel clot end point, the turbidimetric test and the kinetic chromogenic test. The gel
clot end point is based on the formation of a solid gel
clot. It is an in vitro test for bacterial endotoxins that
does have some advantages, as it is cheap, rapid, simple to perform and sensitive to low endotoxin concentrations. This test is often used by hospital and
small-scale manufacturers and is used as a definitive
test if doubt exists regarding results obtained by the
other test methods.
With the gel clot procedure, a solution containing
the endotoxin is added to a solution of the lysate.
The reaction r equires a proclotting enzyme system
and a clottable protein coagulogen that are provided
by the lysate. The reaction that takes place is shown
in Figure 38.3. The rate of this reaction is affected
by several factors, including the concentration of
endotoxin , the pH and the temperature. In the test
procedure, the lysate is mixed with an equal volume
of the test s olution in a depyrogenated container,
such as a glass tube. The tube is then incubated
undisturbed at 37
C for a period of about 60 minutes. The test is a pass or fail test. The end point is
identified by gently inverting the glass tube. A positive result is indicated by the formation of a solid
clot of coagulin. This clot does not disintegrate when
thetubeisinverted.Anegativeresultisindicatedif
no gel clot has been formed. This test needs appropriate positive and negative controls. For a positive
control, a known concentration of endotoxin is
added to the lysate alone and then repeated with a
product sample. As a negative control, water that is
free of endotoxin is added to the lysate. All the
controls must produce appropriate results for the
test to be valid. The sensitivity of the assay is limited
by the sensitivity of the lysate used in the test. The
gelclottestwilldetectbetween0.02and1.0
Bacterial endotoxin tests
This test, as detailed in Appendix XIV of the BP
(2007), is commonly referred to as the limulus amoebocyte lysate (LAL) test. It detects or quantifies
endotoxins from Gram-negative bacteria. The BP test
allows the use of a lysate of amoebocytes from either
the American or Japanese horseshoe crab. Not surprisingly, however, in practice the lysate used in tests
in Europe and North America is obtained from amoebocytes of the American horseshoe crab Limulus
polyphemus, while the lysate of the Japanese crab
(Tachypleus tridentatus) is used in tests carried out
in Asia. Although six tests are detailed in the BP
(2007), these tests can be grouped into one of three
Figure 38.3*The lysate clotting mechanism.
417
SECTION FOUR Dispensing and related pharmaceutical practice activities
endotoxin units per milli litre. Some recently developed biopharmaceuticals have shown similar activity
to endotoxin in this and t he other endotoxin tests.
Before this test is carried out, it is necessary to
determine that:
*
The test equipment does not adsorb endotoxins
*
The lysate is of suitable sensitivity
*
No interfering agents are present.
The turbidimetric test is used in the testing of water
systems and for testing simple pharmacy products.
The test measures the opacity change in the LAL test
due to the formation of insoluble coagulin. An increase in the endotoxin concentration produces a proportional increase in opacity due to the precipitation
of the clottable protein coagulin.
The kinetic chromogenic test is an automated
test used by commercial parenteral manufacturers
to test large numbers of complex products. The test
gives an accurate result over a wide range of endotoxin
concentrations. The test measures the co lour
change induced by the rel ease of the chromogenic
chemical para-nitroanilide. This is released as a
by-product of the clotting reaction during the
LAL test. The quantity of para-nitroanilide produced is directly proportional to the endotoxin
concentration.
Pyrogen testing
The BP pyrogen test involves measuring the rise in
body temperature of healthy mature rabbits. This
temperature rise is recorded after the rabbits have
been intravenously injected with a sterile solution of
the test substance. The environment and the equipment used in the test are detailed in the BP (2007).
This test can only be carried out where the rabbits can
tolerate the test product.
The test itself is preceded by a preliminary test to
identify and exclude any animal with an unusual response to the trauma of the injection. With the preliminary test, a warmed pyrogen-free saline solution is
injected into the rabbits. The temperature of the rabbits is recorded from 90 minutes before the test to
3 hours after the injection, as specified in the BP
(2007). The fever response in the rabbits after the
injection with pyrogens follows a biphasic response.
After the injection, there is a lag time of about 15–18
minutes, which is followed by a rapid temperature
rise to a peak within 2 hours. The temperature then
falls and is followed by a second rise in temperature.
This returns to normal after 6–9 hours. False-positive
temperature increases occur with rabbits as a result
of:
*
Injury
*
Badly positioned recording devices
*
Distress.
The rabbits may develop a resistance to pyrogens. As a
result, they are tested at specified time intervals.
Depyrogenation
Depyrogenation is the elimination of all pyrogens
from the production materials, solutions and equipment. It is achieved by either removal or inactivation
of the pyrogens. The main method of preventing pyrogens contaminating parenteral products is strict control of the ingredients used. That is solvents, raw
materials, packaging materials and equipment should
not be contaminated with pyrogens.
A simple m ethod of removing small amounts of
pyrogens from surfaces such as packaging components is by rinsing the surfaces with non-pyrogenic
water. As pyrogens are non-volatile, distillation is
the principal method of avoiding contamination of
water used in parenteral products. Th is is achieved
by positioning a trap, fitted with baffles, in the still.
The trap remov es the droplets of water by impingement and prevents pyrogens being carried over into
the distillate. However, the freshly collected distillate that is initially pyrogen-free water can become
contaminated with organisms and pyrogens if
stored for more than 4 hours at 22
microbialgrowthinthiswater,itmustbesterilized
soon after collection or stored at high temperatures
to suppress microbial growth. Pyrogens can be removed from solutions by ultrafiltration that separates pyrogens by a process based on their relative
molecular mass. This specialized system has been
used to depyrogenate antibiotic products during
their commercial production. These filters are different from the 0.22 mm filters often used in pharmacy production.
Various methods are used to inactivate pyrogens
including heat treatment, acid–base hydrolysis and
oxidation. High temperature is widely used to incinerate pyrogens especially for glassware, thermostable
equipment and formulation components. Dry heat at
C for 30 minutes is normally used. The com-
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monly used dry or moist heat sterilization cycles
(see Aulton 2007) will not greatly reduce the pyrogen
burden of parenteral products.
C. To avoid
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